The original author of most of the code needed to implement this was brian d foy,
who sent this module to me after I complained I didn't have the time to implement horizontal bar charts.
I took the code that lived in here,
and distributed it over axestype.pm and bars.pm,
to allow for a better integration all around.
His code,
in turn,
was mainly based on an earlier version of bars.pm and axestype.pm.